This conventional kind of device, as disclosed in Japanese Utility Model Laid-Open Gazette No. Sho 57-17,893, has (1) first and second operating levers pivotally supported to a fixing member through a lever shaft, (2) one end of a control wire fixed to the first operating lever, and (3) retaining mechanism between the fixing member and each operating lever, which positions and holds one operating lever at the operating position of each operating lever and alternately releases each operating lever from being held.
In the conventional speed control device, when a bicycle derailleur is at, for example, the top position, in order to change the speed to the low position, the first operating lever is turned in the direction of pulling the control wire, whereby the retaining mechanism holding the second operating lever at the top position is released so that the second operating lever returns to the original position by a return spring, and the first operating lever is held at the low position by the retaining mechanism.
The second operating lever at the original position is turned in the same direction as the first operating lever, thereby changing the speed from the low position again to the top position. Hence, the retaining mechanism holding the first operating lever at the low position is released so that the first operating lever is restored by a return spring to the original position and the second operating lever is held at the top position.
Such conventional speed control device, which uses two levers pivoted to the fixing member, is complicated in construction and expensive to produce. Also, since each operating lever is alternately operated, each operating lever, when operated for changing the speed, must be operated by the cyclist changing the position of his finger. As a result, it is troublesome for him to search for the position of the operating lever upon each operation.